1. Field of the Invention
The present invention relates to an image forming process, an ink set, an image formed by the ink-jet method, a recorded article, a surface-treated article and a surface treating process.
2. Related Background Art
The ink-jet recording method conducts recording by ejecting ink to apply the ink onto a recording medium such as paper. It is easy to realize a head having high-density multi-orifice with ease, and formation of images of high-resolution and high-quality at high speed by using an ink jet recording method where an ink droplet is ejected by the actin of a bubble formed in the ink by applying thermal energy to the ink by using an electrothermal converter as an ejection-energy supply means as disclosed in, for example, Japanese Patent Publication Nos. 61-59911, 61-59912 and 61-59914.
In general, conventional inks for ink-jet recording contain water as a principal component, and in addition, a water-soluble solvent of a high boiling point such as glycol to prevent drying and clogging at orifices. When such an ink is used for recording on a recording medium, sometimes there arise problems such as insufficient fixation, and uneven image presumably due to the uneven distribution of a filler and/or a size on the surface of the recording medium such as paper.
Besides, image quality as high as the silver salt photograph has recently become required for ink-jet recording, leading to intense technical demands +for high image density, wide color reproduction range and enhanced color evenness on ink-jet recording.
Under such circumstances, various proposals have heretofore been made to stabilize the ink-jet recording process and to enhance the quality of articles recorded by the ink-jet recording process. One of the proposals on the recording medium is to coat the surface of a base paper of the recording medium with a filler and/or a size. For example, there has been disclosed a technique to form an ink receiving layer on the base paper by applying porous fine particles that adsorb a coloring material on the base paper as a filler. Recording media produced by using these techniques are now on market as the ink-jet coating paper etc.
One of the technical proposals on the recording liquid ejected onto the recording medium is application of an ink and a liquid reactive with the ink onto the recording medium in such a manner that the ink reacts with the liquid on the recording medium. Ink-jet printers using this technique are on the market.
More specifically, Japanese Patent Application Laid-Open No. 63-60783 discloses a method in which a liquid composition containing a basic polymer is applied to a recording medium, and an ink containing an anionic dye is then applied thereto, thereby conducting recording. Japanese Patent Application Laid-Open No. 63-22681 discloses a recording method in which a first liquid composition containing a reactive chemical species and a second liquid composition containing a compound reactive with the chemical species are mixed on the recording medium. Further, Japanese Patent Application Laid-Open No. 63-299971 discloses a method in which a liquid composition containing an organic compound having two or more cationic groups per molecule is applied to the recording medium, and recording is then conducted with an ink containing an anionic dye. Japanese Patent Application Laid-Open No. 64-9279 discloses a method in which an acidic liquid composition containing succinic acid or the like is applied to a recording medium, and recording is then conducted with an ink containing an anionic dye.
Further, Japanese Patent Application Laid-Open No. 64-63185 discloses a method in which a liquid composition that can insolubilize dyestuff is applied to the recording medium prior to application of an ink. Further, Japanese Patent Application Laid-Open No. 8-224955 discloses a method in which a liquid composition containing cationic substances different in molecular weight distribution range from each other is used together with an ink containing anionic compound. Japanese Patent Application Laid-Open No. 8-72393 discloses a method in which a liquid composition containing a cationic substance and finely ground cellulose is used together with an ink. In both publications, it is shown that the obtained image is excellent in image density, character quality, water fastness, color reproducibility and bleeding problem. Further, Japanese Patent Application Laid-Open No. 55-150396 discloses a method in which recording is conducted with a dye ink on a recording medium, and a water-proofing agent that forms a color lake with the dye is then applied to make the resulting recorded image water proof.
(1) Study of Images on Coated Paper:
It is well known that the above-described recording medium obtained by coating the surface of the base paper of the recording medium with a filler and/or a size (hereinafter referred to as coated paper) enables formation of high-quality images.
In general, in order to obtain an image of high saturation, it is known that the coloring material should be maintained in a monomolecular film state without aggregation on the surface of the recording medium, for which the porous fine particles on the coated paper serves. However, in order to obtain images of both high density and high saturation with a given ink containing a coloring material, it is indispensable to form an ink-receiving layer as thick as the paper substrate is covered with a large amount of the porous fine particles, thus leading to the loss of the texture of the base paper.
The present inventors thought that reason why such a thick ink-receiving layer is required that the coloring matter is not effectively adsorbed on the porous fine particles.
Following explanation is made assuming coated paper having one ink-receiving layer. FIG. 9 schematically illustrates a section of a coated paper in the vicinity of the surface thereof. In FIG. 9, reference numerals 901 and 903 indicate a base paper and an ink-receiving layer, respectively. The ink-receiving layer 903 comprises porous fine particles 905 and an adhesive (binder) 907 for immobilize particles. When an ink is applied to the ink-receiving layer 903, the ink penetrates into the voids between the porous fine particles 905 by capillarity to form ink-penetrated portions 909. As illustrated in FIG. 9, since the density of the porous fine particles in the ink-receiving layer varies locally, the mode of ink penetration by capillary phenomenon varies locally. Therefore, the coloring material cannot evenly contact with the surfaces of the porous fine particles in the course of ink penetration, so that the coloring material are not efficiently adsorbed by the porous fine particles.
Further, penetration of the ink is partially inhibited by the adhesive 907, and thus the ink-receiving layer 903 has portions into which the ink could not penetrate and which cannot contribute to coloring. For this reasons, the adsorption of coloring material in a monomolecular state by the fine particles is not efficient compared with the particle amount in the conventional coated paper. As a result, a great amount of the porous fine particles are required to provide a high-quality image, impairing the texture of the base paper.
Based on such a theory as described above, the present inventors have found out that by using a liquid dispersion of fine particles capable of adsorbing a coloring material together with an ink containing the coloring material for effective adsorption of the coloring material onto the particles in a liquid—liquid state, both the density and saturation of the resulting image are enhanced, which leads to the present invention.
(2) Study of Images Formed by Two-Liquid System:
As described above, an ink-jet recording process using an ink and a treating liquid reactive with the ink in combination (hereinafter referred to as “two-liquid ink-jet recording”) is already recognized as an excellent technique which can provide extremely high-quality images irrespective of the kind of the recording medium.
However, further study of this technique by the present inventors has revealed that white stripes may appear in a recorded article depending on the recording conditions. The recent circumstances where image quality comparable to that of the silver salt photography is required for the ink-jet recorded articles has motivated the present inventors to solve this problem. The present inventors have studied further the cause of such white stripes and concluded that the white stripes occur due to the intense reaction between the ink and the treating liquid.
FIGS. 10A to 10C schematically illustrate a presumed phenomenon during two-liquid ink-jet recording on a recording medium to explain the mechanism of white stripes. Assumed is a case where an ink containing an anionic coloring material in an aqueous medium (hereinafter referred to as “anionic ink”) and an aqueous liquid composition containing a cationic substance reactive with the anionic substance (coloring material). The liquid composition 1001 is first applied to the surface of a recording medium 1003 by an ink-jet system. The anionic ink 1005 is then applied to the site on the recording medium, to which the liquid composition 1001 has been applied, so that the ink and the liquid composition come into contact with each other in a liquid state on the recording medium, thereby starting the reaction of the anionic coloring material with the cationic substance. As a result, the liquid medium of the ink and the aqueous medium of the liquid composition penetrate deep into the recording medium, but the coloring material is retained on the surface of the recording medium as an aggregate 1007 formed by the reaction between the cationic substance and the coloring material. Reference numeral 1009 in FIG. 10C denotes the front of the penetrating liquid media.
As described above, in the two liquid ink-jet recording, both high image density and water resistance are achieved by preventing the coloring material from penetrating into the recording medium but retaining it on the surface of the recording medium as much as possible. In the conventional two-liquid ink-jet recording, the general recognition is that image quality is further enhanced by strengthening the reactivity of the ink with the liquid composition as much as possible to make all the coloring material in the ink react with the cationic substance for its retention on the surface of the recording medium.
However, the present inventors have thought that the control of the properties of the ink and the liquid composition based on the above technical idea might suppress the minute feathering around the colored parts or pixels forming the image which leads to occurrence of white stripes in the image, or might cause excessive aggregation of the coloring material which leads to reduction of color saturation of the image. Based on such a prediction and technical consideration, the inventors have carried out various experiments with the expectation that reduction of the reactivity between the two liquids in the two-liquid ink-jet recording can effectively prevent white stripes and can enhance the saturation of the image. As a result, minute feathering could be generated at the peripheries of colored parts or pixels without deteriorating image quality to enhance the saturation of the image.